Sheet drum for a sheet printing press



United States Patent lnventor Appl. No. Filed Patented Assignee Priority SHEET DRUM FOR A SHEET PRINTING PRESS 5 Claims, 3 Drawing Figs.

U.S. Cl 271/51, 101/420 Int. Cl B65h 5/06 Field of Search 271/51; 226/97; 101/420 Primary ExaminerRichard E. Aegerter Att0rney-Hane & Baxley ABSTRACT: There is disclosed a sheet drum of a sheet printing press in which adjacent to the peripheral wall of the drum an air cushion is formed by feeding pressure air into the drum and causing the air to escape from the drum through an air permeable peripheral wall portion thereof. The lifting force of the cushion effects a smooth and uniform separation of the sheets from the peripheral wall of the drum. The area of the air cushion and the lifting force thereof can be conveniently regulated in accordance with the specific requirements of the work to be performed.

Patentea Nov. 21,1970

Inventor: sumac-men bcuuammln QTTORNGYS,

SHEET DRUM-FOR A SHEET PRINTING PRESS The invention relates to a sheet-feeding orconveying device for a sheet printing press and more particularly to a sheet drum including means for separating the sheets from the peripheral wall of the drum by airjets emanating from orifices in the drum wall. Such separation of the sheets fromthe drum wall by air jets is widely used in the sheet printing industry to prevent a direct contact between newly printed sheets and the drum wall as such contact may cause smearing of the print on the sheets.

There are known sheet drums including tubes disposed parallel to the rotational'axis of the drum and provided with apertures for the escape of air. The escape of air through the apertures is so controlled that it is effective only during part of each revolution of the drum. Devices of this kind are dis closed, for instance, in German Pat. No. 465,250.

There are also known sheet-feeding devices in which nozzles move in unison with 'the grippers for the sheets for part of the gripper movement. The airjets discharged from these nozzlcs are intended to effect an unimpeded turning of the sheets. Devices of this kind are described, for instance, in German Pat. No. 576,774.

U.S. Pat. No. 2,730,950 discloses a device in which sheet guiding rings on a skeleton drum each have on their peripheral wall a perforated tube to which pressure air is supplied.

The briefly aforedescribed conventional sheet-feeding devices have in common that the air emanates from a com partitivcly small number of nozzles and orifices. Accordingly, the sheets are separated from the wall of the drum by the impact of a number of localized air jets directed against the surface of the sheets. Experience and tests have shown that the use of such localized airjets entails serious disadvantages. The spacings between the jets or orifices unavoidably cause cross flows and eddy currents and such air disturbances nullify, to a certain extent, the desired lifting effect of the airjets. Even the provision of a great number of orifices or nozzles per unit of wall surface of the drum and a uniform distribution of such orifices and nozzles eliminate the occurrence of air disturbances only to a limited extent and do not produce a uniform distribution of the lifting force over the entire area of the sheets and hence, the desired smooth movement of the sheets, without flutter. The manufacture of a drum having a great number of orifices in its peripheral wall or the installation of a great number of nozzles is expensive. Moreover, the required volume of pressurized air increases with an increase in the number of orifices or nozzles, the more so, as there is a practical limit to the minimum size of the orifices or nozzles. Obviously, an increase of the required supply of air increases correspondingly the costs of the printing press operation. It is also not desirable to infuse a high volume of air between the drum and the sheets as such high volume is difficult to control.

It is a broad objectof the invention to provide a novel and improved sheet drum of the general kind above referred to in which thc'sheets are separated from the peripheral wall of the drum by a continuous air cushion rather than by localized air jets emanating from orifices or nozzles in the drum wall. The use of such air cushion has the advantage that the sheets are supported on their entire area and thus uniformly and smoothly lifted away from the drum wall.

A more specific object of the invention is to provide a novel and improved sheet drum in which the lifting force exerted by the air cushion can-be conveniently regulated in accordance with the size and the stiffness of the sheets.

Another more specific object of the invention is to provide a novel and improved sheet drum in which the area of the peripheral drum wall contiguous to which the air cushion is formed, can be conveniently varied in accordancewith the specific requirements of the work to be performed The aforepointed-out features, objects and advantages and other features, objects and advantages which will be pointed out hereinafter are obtained by making at least part of the peripheral wall of an air permeable or porous material. Such materials may be sintered materials or porous plastics. There are known and available in the market, porous materials which include a multitude of pores having a width of about 25 ,u. Material of this kind hasbeen found to be particularly use ful.

Air percolating through the multitude of pores in the material forms a thin air -cushion between the peripheral wall of the drum and sheets placed thereupon thereby effectively preventing a smearing of fresh print. As is evident, an air cushion as described does not have the localized impact action as unavoidably caused by airjets.

According to one aspect of the invention, the drum may have double walls radially spaced from each other. The annular space thus formed within the drum is divided by lengthwise elongate ribs into a plurality ofclosed compartments or chambers alined parallel to the rotational axis of the drum. in this manner a plurality of porous wall areas are formed each suhtended by a closed chamber thus making it conveniently possible to effect a uniform escape ofair from the it all of the drum. Moreover, the division of the air space within the drum into separate chambers permits a control of the supply of air to the individual chambers.

The invention also includes the provision ofcontrol means for supplying the individual chambers successively with pres sure air for part ofa revolution of the drum. The subdivision of the space within the drum into several chambers and the control of the air supply to thechambers reduce very considerably the required total volume of pressure air as during each revolution of the drum only those areas ofthc drum wall must be supplied with air with which a sheet will come in contact while passing the drum.

As is evident, the area ofthe drum to which air must be supplied increases gradually as a sheet is moved into coaction with the drum until this area corresponds to at least the size of the sheet. The required area similarly gradually decreases as the sheet moves out of coaction with the drum.

According to the invention, control of the angle of rotation during which the individual chambers of the drum are supplied with air can be conveniently varied by adjustment of rings or sleeves arranged for controlling the air supply to the drum. The beginning and the end of the discharge of air from the drum can thus be selected in accordance with the weight and the stiffness of the sheets thereby controlling the sheets during the movement thereof into coaction with the drum and during movement out of such coaction.

The invention also contemplates the provision of slides by means of which the feed of air to the individual chambers can be throttled or interrupted.

Parts of the porous drum wall which will, in any event, not come in contact with sheets can be closed off by the slides from the supply of air. Such situation occurs, for instance, when small-sized sheets are to be conveyed by the drum. Similarly, the feed of air to other parts of the drum can be throttled or interrupted if such partial throttling or interruption of the flow results in a smoother movement of the sheets in a specific operation.

In the accompanying drawing a preferred embodiment of the invention is shown by way of illustration and not by way of limitation.

In the drawing:

FIG. 1 is a lengthwise sectional view of a drum according to the invention;

FIG. 2 is a section taken on line 11-" of FIG. 1; and

FIG. 3 is a section taken on line III-III of FIG. 1.

Referring now to the figures more in detail, the exemplified drum comprises a shaft 1 which is suitably journaled in sidewalls 4 and 5 of the frame structure of a sheet printing press by bearings 2 and 3 such as ball bearings. The shaft has keyed or pinned thereupon a gear 6 which should be visual ized as being coupled by a chain drive to a motor (not shown). The sheets to be layed out by the'drum are gripped by gripper assemblies mounted on endless chains and guided about the drum. The sheet transport means should be visualized as being conventional and does not constitute part of the invention. Accordingly, it is not shown except for gears 12 and 13 which are keyed or pinned to shaft 1.

The shaft seats annular housings l4 and which are rotatable on the shaft. Roller or ball bearings 16 to 19 are preferably interposed between the housing and the shaft. The housings have in one of their sidewalls openings 20 and 21 respectively. These openings communicate with feed ducts 22 and 23 secured to the housings. for instance, by screw connections. The feed ducts serve to feed pressure air into the housings and are connected to a suitable source of pressure air (not shown). The feed ducts and thus the annular housings 14 and 15 are secured by screw bolts 24 and 25 to the sidewalls 4 and 5 of the press. The peripheral wall of each of the housings is covered by an inner cover ring 28 and 29 respectively. detachably secured to the housings by screws 26 and 27 respectively. The peripheral housing walls and the inner cover rings each include peripherally elongate slots 30. 31 and 32. 33 respectively as can best he seen in FIG. 2. These slots permit a radially directed discharge of air from the housings. The

effective areas for the escape of air can be varied by turning cover rings 28 and 29 with reference to housings 14 and 15 within the limits set by peripherally elongate slots 11 through which the screws 26 and 27 engage the housings.

Shaft 1 further seats pinned or keyed thereto outer cover rings 34 and 35 respectively. These rings have apertures 36 and 37 respectively in their peripheral walls and are slidable on inner cover rings 28 and 29 respectively. Accordingly, outer cover rings 34 and 35 open during that part of their rotation about the inner cover rings 28, 29 respectively and housings 14,15 respectively during which openings 36 and 37 of rings 34 and 35 respectively are in registry with slots 30, 31, and 32, 33, passages for a radial air flow via ducts 22, 23; openings 20, 21 and housings 14, 15 into chambers 42 and 43. These chambers, which can be best seen in H0. 2, are defined by walls or ribs 42a secured by screws 38 and 41 to the peripheral wall ofouter cover rings 34 and 35 respectively and extend lengthwise parallel to shaft 1 in circumferentially spaced relationship. They are peripherally open for a purpose which will be more fully explained hereinafter.

Slides 44 and 45 on the upstream side ofopenings 36 and 37 in outer cover rings 34 and 35 serve to control the flow of air into the chambers by throttling or cutting off the air supply by varying the positions ofthe-slides.

As is shown in FlG. 1, the chambers 42 and 43 are gradually reduced in radial width toward the middle of the length of the shaft between housings 14 and 15. The radially inner walls of the chambers are secured at the point at which chambers 42 and 43 meet by screws 39 and 40 to a support bracket 61 pinned or keyed upon the shaft.

The outer walls of the chambers are closed off by a cover 46 formed by an air permeable material such as a suitable fabric, porous plastic material of sufficiently porous sheet metal. Cover 46 is secured to angle brackets 53 to 56 which, in turn, are secured by screws 47 to 52 to the brackets and the housings, at least some of the screws being preferably countersunk.

A further porous cover 57 such as a sheet made of a porous plastic such as Perlon is stretched over cover 46.

As is evident from the previous description and also from FIG. 1, pressure air fed into the chambers 42 and 43 is uniformly distributedover the length of the drum and escapes therefrom in radial direction through the multitude of pores in cover sheets 46 and 57. Accordingly, a thin air cushion is formed contiguous to the respective peripheral wall area of the drum to prevent, as previously described, a direct contact between the drum wall and the sheets.

As is evident from Fig. 2, the weight of the chambers causes a certain unbalance of the structure as the chambers do not encompass the entire peripheral wall of the drum. Such unbalance is compensated by a counterweight 60.

While the invention has been described in detail with respect to a certain now preferred example and embodiment of the invention, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended. therefore. to cover all such changes and modifications in the appended claims.

I claim:.

1. A sheet-feeding device for a sheet printing press. said device comprising in combination:

a rotary drum having two radially spaced-apart peripherai walls defining therebetweeh an annular space within the drum, the outer one of said peripheral walls being made at least partly ofair permeable material;

partition walls extending between said drum walls and rotat ing in unison therewith, said partition walls dividing said space into a plurality of rotating chambers closed against each other.

pressure air supply means for supplying pressure air to said Chambers to form by air escaping from the chamber through said air permeable peripheral wall an air cushion adjacent to said wall for'lifting sheets placed upon the outer wall clear of contact with the same; and

control means controlling said air supply means for connecting the same successively to said chambers while rotating in unison with the drum whereby each chamber is supplied with pressure air only for part of a revolution of the drum.

2. The device according to claim 1 wherein said partition walls comprise axially disposed elongate ribs dividing said space into lengthwise parallel and circumferentially-spaced chambers.

3. The device according to claim 1 and comprising slide means interposed between said air supply means and each of said chambers, the positions of said slide means controlling the volume of air supplied by the air supply means to the respective chamber.

4. The device according to claim 1 wherein said control means comprise adjustable means interposed between said air supply means and saidchambers, said adjustable means including two relatively rotatably members each having an opening therethrough, the angular positions ofthe openings in said members relative to each other controlling passageways for the flow of pressure air to the chambers and thus the rotational angle of the drum during which the chambers are supplied with air.

5. A sheet-feeding device for a sheet printing press. said device comprising in combination:

a rotary drum having two radially spaced-apart peripheral walls defining therebetween an annular space within the drum, the outer one of said peripheral walls being made at least partly of air permeable material;

partition walls rotating in unison with the drum and dividing said space into a plurality of chambers closed against each other;

air supply means for supplying pressure air to said chambers to form by air escaping from the chambers through the air permeable outer wall an air cushion adjacent to said outer wall for lifting sheets placed upon said wall clear of contact with the same; and

control means controlling said air supply means for connecting the same successively to said chambers whereby each chamber is supplied with pressure air only for part of a revolution of a drum, said control means comprising adjustable means interposed between said air supply means and each of said chambers, said adjustable means including concentric sleeves each having an aperture in its wall, said sleeves being rotatably adjustable with reference to each other whereby by varying the relative angular position of the sleeves the timing of the feed of air to the chambers and thus the rotational angle of the drum during which the chambers are supplied with air are changed. 

